a semantic transformation approach for iso 15926

A Semantic Transformation Approach for ISO 15926

Sari Hakkarainen1, Lillian Hella1, Darijus Strasunskas1 and Stine Tuxen2

1Norwegian University of Science and Technology (NTNU), NO-7491, Trondheim, Norway {sari, hella, dstrasun}@idi.ntnu.no

2Bekk Consulting AS, NO-0150 Oslo, Norway

[email protected]

Abstract. Traditional industries anticipate supporting cross-organizational co-operation as applied in the semantic Web and Web services environments. However, the international standards used in organisations are often developed prior to or independent from the novel technologies. We demonstrate a solution, namely to perform controlled semantic transformations enabling both technolo-gies. A study in the semantic relationship between an international standard, ISO 15926 Part 2, and a semantic Web technology, OWL DL is reported. Three alternative semantic transformation approaches are identified where two are elaborated further. Accordingly, two Transformation Protocols are developed in order to transform ISO 15926 components to OWL. Further, two Inverse Trans-formation Protocols are developed. The transformations are analysed and the al-ternative transformation protocols are evaluated

1 Introduction

There is a need for efficient sharing and usage of information. Large traditional indus-tries, such as oil industry are dependent on internationally agreed standards to main-tain a semantically equal understanding of shared domains in and across organiza-tions. However, the international standards currently used are often developed prior to or independent from the novel technologies. One possible solution is to develop a language that is powerful enough to express and differentiate the technological ele-ments as well as the underlying semantics. A further requirement here is that the lan-guage must be computer and human readable. An initiative to translate the interna-tional standard ISO 15926 to the semantic Web technology OWL has been taken by the Norwegian Oil Industry1. Here we study and demonstrate an alternative solution, namely to facilitate controlled semantic transformations for models enabling co-existence of both technologies. The semantic relationship between the ISO 15926 Part 2 and OWL DL is studied in particular. The objective is to study the semantic rela-tionship between ISO 15926 and OWL in order to facilitate in- and cross-organizational co-operation as applied in the semantic Web and Web Service envi-ronments.

1 Integrated Operations at OLF – Norwegian Oil Industry Association, http://www.olf.no

2 Hakkarainen et al.

Two alternative transformation protocols are defined. Further, in order to examine possible loss of semantics during the transformation two inverse transformation pro-tocols are defined. The transformations and the inverse transformations are analysed and the alternative transformation protocols are evaluated comparatively by their semantic performance.

The outline is as follows. In section 2, the studied representations and related work are described and the prerequisites presented. In section 3, transformation and inverse transformation protocols are defined. In section 4, the alternative protocols are ana-lysed and the ability to preserve semantics is compared between the approaches. Fi-nally, in section 5, conclusions and directions for future work are discussed.

2 Describing the Semantics

The diversity and multitude of resources and applications in organizations and the Internet places elaborated requirements on methods and tools for efficient generation, manipulation and compositional usage of information and services. OWL and ISO 15926 that are in the foci of this study are representing the novel models for reasoning about and for specifying information systems, respectively.

2.1 ISO 15926

The purpose of the international standard for Industrial automation and integration – Integration of life-cycle data for process plants including oil and gas production facili-ties (ISO 15926) is to facilitate integration of data to support the life-cycle activities and processes of process plants. It has defined syntax and graphical representation yet not formal semantics. It is built on EXPRESS (ISO 10303-11) to specify its data model yet facilitates more accurate distributed specification.

ISO 15926 consists of seven parts as follows. 1 - Overview and fundamental prin-ciples; 2 - Data model; 3 - Methodology for the development and maintenance of reference data libraries; 4 - Reference data; 5 - Procedures for registration and main-tenance of reference data; 6 - Scope and methodology for developing additional refer-ence data; 7 - Implementation methods for data exchange and integration.

ISO 15926 Part 2 [9] specifies a data model that semi-formally defines the mean-ing of the life-cycle information in a single context supporting the views that process engineers, equipment engineers, operators, maintenance engineers and other special-ists may have on the plant [8]. Table 1 summarizes the main components.

Table 1. Components of ISO 15926 Part 2

ISO 15926 Comment Main components Entity data type The standard consists of 201 Entity data types, the top level Entity data type is

thing, with its subtypes possible_individual and abstract_object. All other entities are subtypes of these.

Attribute Each Entity data type can have Attributes that are specified in the Attribute definition part of the description of an Entity data type.

A Semantic Transformation Approach for ISO 15926 3

Entity data type restriction Subtype Subtype is specified before “is a” in the textual description of an Entity data

type. All the Entity data types are part of a Subtype-Supertype hierarchy. Supertype Supertype is specified after the “is a” in the textual description of an Entity

data type. All the Entity data types are part of a Subtype-Supertype hierarchy. One-of Entity data types can be mutually exclusive, and this is specified in the textual

description of an Entity data type. Transitivity An Entity data type can be defined as transitive, referred to as Transitivity. Attribute restrictions Attribute-belongs-to An Attribute can not exist independently from an Entity data type. The Entity

data type that defines an Attribute within an Attribute definition is specified through Attribute-belongs-to.

Attribute-relates-to An Attribute can relate an Entity data type to either another Entity data type or Simple Type. The related Entity data type or Simple Type is specified through Attribute-relates-to.

Redeclared Attribute-relates-to

An Attribute-relates-to is re-declared when it relates to a different Entity data type than its Supertype Entity data type does, i.e. Redeclared Attribute-relates-to.

Simple types STRING STRING is a Simple Type, defined in ISO 10303-11:1994 INTEGER INTEGER is a Simple Type, defined in ISO 10303-11:1994 REAL REAL is a Simple Type, defined in ISO 10303-11:1994 LOGICAL LOGICAL is a Simple Type, defined in ISO 10303-11:1994 BOOLEAN BOOLEAN is a Simple Type, defined in ISO 10303-11:1994 BINARY BINARY is a Simple Type, defined in ISO 10303-11:1994

2.2 Prerequisite for the analysis

Semantic Web technologies allow the definition of logical relationships against which reasoning can occur, something EXPRESS does not fully support. EXPRESS does not formally distinguish between attributes and relationships [12], a feature that is often required. Hence, a transformation from ISO 15926 to an ontology language is antici-pated to facilitate reasoning.

OWL was chosen as an ontology language for transformation being a recommen-dation by W3C showing its relative maturity level and suitability for Web applica-tions. Furthermore, OWL version of ISO 19526 is recommended by [12] since OWL offers the capability to better connect with models of individuals and ontologies. It also offers potential for enhanced distribution of the models through namespace refer-encing. However, transformation form ISO 15926 to OWL requires a semantic trans-formation protocol that is controlled and based on semantics.

2.3 Related work

The long-term objective for the work is to establish a semantic relationship between ISO 15926 and OWL in order to facilitate in- and cross-organizational co-operation in traditional domains as applied in the novel semantic Web and Web Service environ-ments. The semantic gap between ISO 15926 and OWL is seemingly narrow when considering the object model part of the languages.

The models in the traditional modelling standards such as ISO 15926 have been used for human interpretation with graphic representation and semi-structured docu-


mentation. The emerging semantic Web recommendations such as OWL are primarily intended for machine interpretation, enabled utilizing the high expressiveness of the syntax when modelling. Thus, the target models should contain more semantics than can be captured in a pure syntactic transformation process and further, a simple 1:1 mapping between language constructs introduce non-intended semantics to the target model. This problem has not been recognized in the current body of related work.

The Integrated Information Platform (IIP) project [10] extend and formalize ISO 15926 using OWL. OWL Full is chosen for maximum expressiveness in the resulting representation [3]. The POSC Caesar2 Intelligent Data Sheet (IDS) project defines product models for data sheets based on ISO 15926 Part 4. A resulting Reference Data Library (RDL)3 is planned to consist of approx. 100,000 EXPRESS standard classes, be defined in ISO 15926 Part 4, and mapped to Part 7 OWL format.

Further, there are efforts to formalize and ontologize other international standards. [4] for instance, have taken an approach to ontologize Electronic Data Interchange (EDI), i.e. to model meaning of the messages and create semantically enabled mes-sages yet maintaining backward compatibility to traditional systems. [6] specifies an OWL ontology to cover the Geographic Information – Metadata (ISO 19115) stan-dard, simply expressing each ISO 19115 as a single OWL construct. These concurrent approaches seek to define a new language in OWL and assume a 1:1 relationship between the languages not considering the problem of general modelling purpose and style.

In order to capture as much of the semantics in the source models as possible, we use production rules that operate on syntactic markers in the model and produce target syntax that not always correspond to the source syntax, but try better to transmit its semantics. In a real world application, we picture the process to be semi-automated, where the user has the possibility to add semantics that was not in the original model but is considered its intention. Syntactic markers for such intention may be found e.g. in natural language (NL) comments and other documentation. NL requires a user to interpret it, but in the future, an automated NL process can be tailored for interpreta-tion in individual domains and application areas. In this way, we expect more of the intended semantics to be preserved, semi-automatically with low labour intensiveness.

A first step in the direction of achieving that long-term objective, namely a study of possible approaches for transformation of ISO 19526 into OWL with high preser-vation of human interpreted semantics is presented in the sequel.

3 Semantic Transformations

A method for transforming the basic components of ISO 15926 to their proper repre-sentation as language constructs in OWL is required. [5] identifies three distinct ways to perform the transformation, all of which have different interpretations and conse-quences for the preservation of semantics in the resulting data models. Two of them are described below, since the third requires access to domain models. Here, only the

2 http://www.posccaesar.com

3 http://www.infowebml.ws


transformation and inverse transformation protocols resulting from respective meth-ods are discussed, the algorithms for actually performing the transformations are described in [5] in detail and the transformations are illustrated by examples.

A transformation protocol consists of a set of transformation rules that define a mapping between a source and one or many target language constructs with an asso-ciated transformation condition that defines complex rules, if any. In the transforma-tion (and inverse) protocol tables below, the first columns specify the source and the second specify the target. The last columns specify transformation conditions being empty when a construct can be transformed unconditionally. Further, a source con-struct is NOT MAPPED if no target construct to represent the source exists. A transfor-mation is IMPLICIT if a source construct is indirectly transformed to a target construct through transformation of other constructs.

3.1 Transformation and inverse using method TM1

Transformation method one (TM1) considers the semantic interpretation of the source language construct when defining a transformation rule to a target construct. Basi-cally, one ISO 15926 component corresponds to exactly one OWL primitive. The assumption is that there exists a one-to-one relationship between the models. The inverse transformation (ITP) using the TM1 method is based on the OWL constructs that the transformation protocol TM1-TP resulted in, i.e. only the language constructs occurring as target in TM1-TP are assigned transformation rules in TM1-ITP. The set of possible target constructs in TM1-ITP is not restricted by the results of using TM1-TP.

Table 2. Transformation protocol TM1-TP

ISO 15926 OWL Transformation condition Main components Entity data type owl:Class

owl:DatatypeProperty IF Attribute relates Entity data type to a Simple Typeowl:ObjectProperty IF an Attribute relates an Entity data type to another

Entity data type AND NOT already translated

Attribute

IMPLICIT IF already translated Entity data type restriction Subtype rdfs:subClassOf Supertype NOT MAPPED One-of owl:disjointWith Transitivity owl:TransitivePropertyc Functional owl:FunctionalPropertyd Attribute restrictions Attribute-belongs-to rdfs:domain Attribute-relates-to rdfs:range IF NOT already translated IMPLICIT IF already translated Redeclared Attrib-ute-relates-to

owl:allValuesFrom

Simple types STRING xsd:string INTEGER xsd:integer REAL xsd:float LOGICAL xsd:boolean BOOLEAN xsd:boolean


ISO 15926 OWL Transformation condition BINARY xsd:integer

Table 3. Inverse Transformation protocol TM1-ITP

OWL ISO 15926 Transformation condition owl:Class Entity data typea rdfs:subClassOf Subtype owl:disjointWith One-of owl:ObjectProperty Attribute owl:DatatypeProperty Attribute owl:TransitiveProperty Transivityb owl:FunctionalProperty Functionalb owl:allValuesFrom Redeclared Attribute rdfs:domain Attribute-belongs-to rdfs:range Attribute-relates-to xsd:string STRING IF xsd:string is used in conjunction with

owl:DatatypeProperty xsd:integer INTEGER xsd:float REAL xsd:boolean BOOLEAN

3.2 Transformation and inverse using method TM2

Transformation method two (TM2) considers extended semantic interpretation of the source language construct when defining a transformation rule to a target construct. Basically, one ISO 15926 component potentially correspond to several OWL primi-tives and vice versa. The assumption is that there exists a many-to-many relationship between the models. The inverse transformation using the TM2 method is based on the OWL constructs that the transformation protocol TM2-TP resulted in, i.e. only the language constructs occurring as target in TM2-TP are assigned transformation rules in TM2-ITP. The set of possible target constructs in TM2-ITP is not restricted by the re-sults of using TM2-TP.

Table 4. Transformation protocol TM2-TP

ISO 15926 OWL Transformation condition Main components

owl:Classa IF NOT relationship AND NOT Subtype of relation-ship AND NOT EXPRESS_string AND NOT EXPRESS_integer AND NOT EXPRESS _real AND NOT EXPRESS_logical AND NOT EXPRESS_boolean AND NOT EXPRESS_binary

owl:ObjectProperty IF relationship OR Subtype of relationship

Entity data type

owl:DatatypeProperty IF EXPRESS_string OR EXPRESS_integer OR EXPRESS _real OR EXPRESS_logical OR EXPRESS_boolean OR EXPRESS_binary

Attribute owl:DatatypeProperty IF Attribute-relates-to a Simple type AND NOT Attribute-belongs-to relationship AND NOT Attribute-belongs-to a Subtype of relationship AND NOT Attribute content


ISO 15926 OWL Transformation condition owl:ObjectProperty IF Attribute-relates-to an Entity data type AND NOT

Attribute-belongs-to relationship AND NOT Attribute-belongs-to a Subtype of relationship AND NOT Attribute content

IMPLICIT IF Attribute-relates-to relationship OR Attribute-belongs-to a Subtype of relationship or already trans-lated OR Attribute content

Entity data type restriction rdfs:subClassOf IF NOT Entity data type relationship AND NOT

Subtype of Entity data type relationshipSubtype

owl:subPropertyOf IF Entity data type relationship OR Subtype of Entity data type relationship

Supertype NOT MAPPED owl:disjointWith IF NOT relationship AND NOT relationship SubtypeOne-of NOT MAPPED IF relationship OR Subtype of relationship

Transitivity owl:TransitiveProperty Functional owl:FunctionalProperty Attribute restrictions

rdfs:domain IF NOT relationship AND NOT Subtype of relation-ship AND NOT Attribute content

Attribute-belongs-to

IMPLICIT IF NOT relationship OR Subtype of relationship OR Attribute content

rdfs:rangeb IF NOT relationship AND NOT Subtype of relation-ship AND NOT already translated

rdfs:rangeb IF (relationship OR Subtype of relationship) AND it is the second Attribute AND NOT already translated

rdfs:domainb IF (relationship OR Subtype of relationship) AND it is the first Attribute AND NOT Attribute-relates-to a Subtype of relationship AND NOT already translated

Attribute-relates-to

rdfs:domainb IF (relationship OR Subtype of relationship) AND the first Attribute AND Attribute-relates-to relationship AND Attribute-relates-to a Subtype of relationship AND NOT already translated

owl:allValuesFrom IF NOT Attribute-belongs-to relationship AND NOT Attribute-belongs-to a Subtype of relationship

rdfs:range IF (Attribute-belongs-to relationship OR Attribute-belongs-to a Subtype of relationship) AND it is the second Attribute

Redeclared Attrib-ute-relates-to

rdfs:domain IF (Attribute-belongs-to relationship OR Attribute-belongs-to a Subtype of relationship) AND it is the first Attribute

Simple types STRING xsd:string

xsd:integer IF NOT Entity data type represen-tion_of_Gregorian_date_and_UTC_time

xsd:gYear IF Attribute year belonging to Entity data type repre-sentation_of_Gregorian_date_ and_UTC_time

xsd:gMonth IF Attribute month belonging to Entity data type representation_of_Gregorian_date_and _UTC_time

xsd:gDay IF Attribute day belonging to Entity data type repre-sentation_of_Gregorian_date_ and_UTC_time

INTEGER

xsd:time IF Attribute hour belonging to Entity data type repre-sentation_of_Gregorian_date_and_UTC_time AND Attribute second NOT already translated AND Attrib-ute minute NOT already translated THEN Attributes second, minute and hour are translated


ISO 15926 OWL Transformation condition xsd:time IF Attribute minute belonging to Entity data type

representation_of_Gregorian_date_and_UTC_time AND Attribute second NOT already translated AND Attribute hour NOT already translated THEN Attribut-es second, minute and hour are translated

xsd:float IF NOT Entity data type representa-tion_of_Gregorian_date_and_UTC_time

REAL

xsd:time IF Attribute second belonging to Entity data type representation_of_Gregorian_date_and_UTC_time AND Attribute minute has not been translated AND Attribute hour has not been translated THEN Attribute second, minute and hour are translated

LOGICAL xsd:boolean BOOLEAN xsd:boolean BINARY xsd:integer

Table 5. Inverse Transformation protocol TM2-ITP

OWL ISO 15926 Transformation condition owl:Class Entity data typea

Entity data type IF relationship OR subPropertyOf relationshipowl:ObjectProperty Attribute IF NOT relationship AND NOT subPropertyOf

relationshipEntity data type IF EXPRESS_string OR EXPRESS_integer OR

EXPRESS_real OR EXPRESS_logical OR EXPRESS_boolean OR EXPRESS_binary

owl:DatatypeProperty

Attribute IF NOT EXPRESS_string AND NOT EXPRESS_integer AND NOT EXPRESS_real AND NOT EXPRESS_logical AND NOT EXPRESS_boolean AND NOT EXPRESS_binary

rdfs:subClassOf Subtype owl:subPropertyOf Subtype owl:disjointWith One-of owl:TransitiveProperty Transivityb owl:FunctionalProperty Functionalb owl:allValuesFrom Redeclared Attribute

Attribute-belongs-to IF NOT used in conjunction with owl:ObjectProperty relationship AND NOT used in conjunction with subPropertyOf owl:ObjectProperty relationship

rdfs:domain

Attribute-relates-to IF used with owl:ObjectProperty relationship OR used in conjunction with a subPropertyOf owl:ObjectProperty

rdfs:range Attribute-relates-to xsd:string STRING IF xsd:string is used in conjunction with

owl:DatatypeProperty xsd:integer INTEGER xsd:float REAL xsd:boolean BOOLEAN xsd:gYear/gMonth/gDay INTEGER

INTEGER IF hour specified by hh OR minute specified by mm

xsd:time

REAL IF second specified by s.sss


3.2 Assumptions underlying the transformation protocols

The transformation protocols above are defined using two transformation methods based on semantic and extended semantic interpretation. Accordingly, there is a need to report the underlying assumptions made for the actual interpretations in this study. A trial transformation was performed in order to assure the quality of the proposed transformation protocols. Some basic assumptions underlying the transformation rules of the above TM1-ITP, TM1-ITP, TM2-TP and TM2-ITP are described in the sequel.

Thing. Every individual in OWL is a member of the class owl:Thing. Thus each user-defined class is implicitly a subclass of owl:Thing [11]. Similarly, ISO 15926 consists of 201 hierarchically ordered Entity data types, with thing on top. Thing has six Attributes. The transformation protocols TM1-TP and TM2-TP map these Attributes to owl:ObjectProperty or owl:DatatypeProperty. Note that OWL does not allow relating properties to owl:Thing. Thus, Entity data type thing is mapped to owl:Class thing which is a subclass of owl:Thing. Further, an Attribute is mapped to owl:ObjectProperty or owl:DatatypeProperty with the associated Attribute-belongs-to thing mapped to rdfs:domain thing. These mappings preserve the one-to-one mapping of the TM1 method.

Identical name for Entity data type and Attribute. Some of the ISO 15926 Attributes are given lexically identical names to some ISO 15926 Entity data types. OWL does not allow identical names for owl:Class, owl:ObjectProperty and owl:DatatypeProperty. In the transformation algorithms in [5] this conflict is simply resolved by starting an owl:Class with a capital letter, whereas starting owl:ObjectProperty and owl:DatatypeProperty instantiations with a lower case letter.

Multi-use of properties. Some ISO 15926 Attributes are used in conjunction with several ISO 15926 Entity data types as Attribute-relates-to with Attribute. A multi-use of properties arises. OWL does not allow creating owl:ObjectProperty with identical names. While resolving this conflict the reasoning capabilities of OWL should be as defined for OWL DL, whereas the semantics in ISO 15926 should be preserved. Thus the transformation conditions in TM1-TP and TM2-TP above assert that such an Attribute or Attribute-relates-to is not directly mapped if a respective Entity data type or Attribute with identical name is already transformed. Note that lexically identical Attributes are used in conjunction with lexically identical Attribute-relates-to. In [5] the specific conditions are exemplified for each of the multi-used properties.

An alternative resolution is to rename the lexically identical Attributes in order to translate each Attribute independently. This strategy is used once where TM1-TP re-names the Attribute content that is an Entity data type subtype. The exception was neces-sary since Attribute-relates-to used in conjunction with Attribute content relates to differ-ent Simple Types for each Entity data type.

Redeclared Attribute-relates-to. An attribute of an Entity data type may be redeclared for a Subtype of that Entity data type. Here the Attribute-relates-to is a different Entity data type than its Supertype Entity data type. The term Redeclared Attribute-relates-to is used to denotate these components.

TM1-TP maps Redeclared Attribute-relates-to to owl:allValuesFrom, while TM2-TP maps it to either owl:allValuesFrom, rdfs:domain or rdfs:range. The inverse trans-


formation protocols TM1-ITP and TM2-ITP map owl:allValuesFrom to Attribute-relates-to. Further, TM2-ITP assures that the Redeclared Attribute-relates-to that in TM2-TP is mapped to rdfs:domain or rdfs:range is inverse mapped to Attribute-relates-to. Thus, much of the semantics is preserved. However, Redeclared Attribute-relates-to will no longer be explicitly defined. Instead an Attribute of an Entity data type, and not only a redeclared one, is defined in the Entity data type. Thus, by comparing an Entity data type with its Subtype it is possible to infer whether Attribute-relates-to is redeclared for the Attributes belonging to its Subtypes.

INTEGER and BINARY. TM1-TP maps both ISO 15926 INTEGER and BINARY to OWL xsd:integer. In the inverse TM1-ITP xsd:integer is mapped to INTEGER. As a consequence, the declarative semantics of BINARY is lost and the number of instances of INTEGER is increased after an inverse transformation.

An alternative strategy would be to map the ISO 15926 Simple type BOOLEAN to xsd:boolean, xsd:hexBinary or xsd:integer. However, xsd:boolean restricts the binary values to 1 or 0 whereas binary may be any combinations of 1 and 0’s, and further, xsd:hexBinary represents the binary digits as hexadecimal digits. The loss of seman-tics occurs even here; TM1-TP maps ISO 15926 BINARY to xsd:integer.

BOOLEAN and LOGICAL. Both ISO 15926 BOOLEAN and LOGICAL are translated to OWL xsd:boolean. The inverse maps xsd:boolean to BOOLEAN. Thus, the declarative semantics of LOGICAL is lost and the number of instances of BOOLEAN is increased.

Fig. 1. Summarizing overview of TM1-TP and TM1-ITP


4 Semantic Analysis of Transformation Methods

4.1 Preserved and altered semantics using TM1

TM1 is summarized in Fig.1. 16 ISO 15926 components are mapped to 14 OWL lan-guage constructs. The overall mapping is straightforward. The detected deviations are described below.

IMPLICITLY translated components. Both Attribute and Attribute-relates-to may be implicitly defined (see Fig.1). Some Entity data types have Attributes with identical names. If the Attribute is already translated we claim that the other Attributes with identical names are implicitly translated through the first Attribute. Further, Attribute-relates-to and Attribute-belongs-to are used in conjunction with the Attribute. If the Attribute is implicitly defined then Attribute-relates-to is also implicitly defined..

NOT MAPPED components. ISO 15926 component Supertype is not mapped in the transformation. ISO 15926 Subtype is translated to rdfs:subClassOf thus automated reasoning is still possible and the semantics is preserved even though Supertype is not mapped.

4.2 Preserved and altered semantics using TM2

TM2 is summarized in Fig.2. According to TM2-TP, ISO 15926 Entity data type is trans-lated to either an owl:Class, an owl:ObjectProperty or an owl:DatatypeProperty.

IMPLICITLY translated components. Both Attribute and Attribute-relates-to may be implicitly defined (see Fig. 2). If it is Attribute content defined inside Entity data type EXPRESS_string, EXPRESS_integer, EXPRESS_real, EXPRESS_logical, EXPRESS_boolean or EXPRESS_binary it is implicitly defined since these Entity data types are translated to owl:DatatypeProperties that relates to the same Simple Type as Attribute content. Even though the semantics of Attribute content are lost, it is of no relevance since it is only used as an intermediary between the Entity data type and the associated Simple Type, while TM2-TP use the Entity data type itself as the intermediary. This rule does only apply when the Attribute belongs to an Entity data type relationship or a Subtype of relationship. Thus, it is a consequence of translating the Entity data type to an owl:ObjectProperty.

When an Entity data type is translated to owl:Class, and its Attributes are translated to owl:ObjectProperties, the owl:Properties are defined independent of the owl:Class. Thus rdfs:domain is used to specify the class that the ObjectProperty belongs to. However, when an Entity data type is translated to owl:ObjectProperty, for example Entity data type classification, its Attributes are not translated, but the value they relate to is specified by rdfs:domain and rdfs:range. Since rdfs:domain and rdfs:range are used inside owl:ObjectProperty it is not necessary to explicitly define the property they belong to.

NOT MAPPED components. ISO 15926 Subtype is translated to rdfs:subClassOf thus automated reasoning is still possible and the semantics is preserved even though Supertype is not directly mapped. When an Entity data type is translated to


owl:ObjectProperty it is no longer possible to define mutually exclusiveness, since OWL does not provide a mechanism for expressing mutually exclusive properties. Hence, the semantics are lost when an ISO 15926 One-of is used in conjunction with an Entity data type translated to owl:Property.

Fig. 2. Summarizing overview of TM2-TP and TM2-ITP

4.3 Comparative analysis of TM1 and TM2

The major difference between TM1-TP and TM2-TP is that TM1-TP only considers the semantics interpretation of the ISO 15926 components, while TM2-TP also considers the semantics of each instance of the components. Consequently a difference is made in the transformation of the ISO 15926 components.

Using TM1-TP, an Entity data type is translated to an owl:Class. Translation of the 201 Entity data types resulted in 201 owl:Class constructs. The resulting OWL code is presented in [5]. In TM2-TP an Entity data type is translated to either owl:Class, owl:ObjectProperty or owl:DatatypeProperty. Translation of the 201 Entity data types resulted in 144 owl:Class, 51 owl:ObjectProperty and 6 owl:DataProperty [5].

Relationship. Entity data type relationship and Subtypes of relationship are translated to owl:Class according to TM1-TP and owl:ObjectProperty according to TM2-TP. When the inverse translations are performed the names of the Attribute is preserved by using TM1-ITP. By using TM2-ITP the Attributes are created, but a new name has to be de-fined as the original names are not used.


By translating Entity data type classification to owl:ObjectProperty classification TM2-TP takes advantage of the reasoning capabilities offered by OWL. However, in addition to loss of Attribute name, semantics concerning the direction of the relation-ship are lost. TM1-TP uses the owl:Class Classification as an intervening class between owl:ObjectProperty classified and owl:ObjectProperty classifier. That is, the proper-ties are connected through classification which provides the direction of the proper-ties. The direction of the relationship is limited in TM2-TP, as illustrated with the one-directional arrow between rdfs:domain Thing and rdfs:range Class. It is possible to extend the Protocol by creating owl:InverseProperty that define the inverse relation-ship.

Attribute. ISO 15926 Entity data type EXPRESS_string, EXPRESS_integer, EXPRESS_real, EXPRESS_logical, EXPRESS_boolean and EXPRESS_binary are translated to owl:Class according to TM1-TP while they are translated to owl:DatatypeProperty according to TM2-TP. The Attribute content is defined within each Entity data type. However, Attribute-relates_to associated with each Attribute relates to different Simple Type components. Thus when the Attributes are translated using TM1-TP it is not possible to take advantage of the OWL feature that allows multiple domains to be defined for an Attribute. As described in section 3.1 TM1-TP renames the Attributes when they are translated to owl:DatatypeProperty.

TM2-TP translates the Entity data types to owl:DatatypeProperty. Thus the Attribute content is lost in the translation. However, the loss of semantics is of no relevance as the Attribute is an intermediary between the Entity data type and the associated Simple Type, while TM2-TP use the Entity data type itself as the intermediary.

The Simple Types. Both TM1-TP and TM2-TP define six Simple Types. While TM1-TP translates these components into four OWL language constructs, they are translated into eight language constructs using TM2-TP. The difference is the translation of the Simple Types used in conjunction with Attribute-relates-to of the Attributes defined within Entity data type representation_of_Gregorian_date_and_UTC_time. Compared to TM1-TP, TM2-TP in a larger extent takes advantage of the language constructs in OWL. However, TM1-TP is preferred if it is necessary to keep hour, minute and second as separate values.

5 Concluding Remarks

Two views for transforming ISO 15926 into OWL are analysed. The first alternative considers the semantic interpretation of the ISO 15926 components straightforward. The second alternative considers extended semantic interpretation, i.e., it also consid-ers the semantics of each instance of the components. A third alternative that is based on contextual semantic interpretation on a domain model was identified in addition yet not further elaborated. The alternative views were tested through definition of alternative transformation protocols with corresponding inverse transformation proto-cols and analysed according to their ability to preserve semantics.

The analysis shows that Transformation Method one (TM1) results in a seemingly direct representation of ISO 15926 in OWL, and enables full specifications, whereas


Transformation Method two (TM2) takes more advantage of the language constructs in OWL. The requirements one places at the resulting OWL representation are deci-sive for selection of a transformation method and for assessing the appropriateness of the proposed transformation protocols. TM1 is most appropriate if the goal is to achieve a representation of ISO 15926 in OWL where the quantity of Entity data types is equal to the number of the corresponding OWL language construct, i.e. where a one-to-one mapping is desired. TM2 is most appropriate if the transformation is performed in order to take advantage of the reasoning facilitates provided by OWL, thus adding functionality not natively present in ISO 15926.

As not having access to complete domain models in ISO 15926, the transformation method three (TM3) fell out of scope for this study. However, the method should be tried out with both semantic and extended semantic transformation method in the future. TM3 is based on the contextual semantic interpretation on existing domain models. A transformation to target language is based on mapping the components of the domain model in source language to semantically equal language constructs in target language. In this case not solely analytic, but empirical observations could be made in conjunction with appropriate statistical analysis.

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a semantic transformation approach for iso 15926

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